Can a Protein Shake Make Me Feel Light Headed and Sick?

If, after drinking a shake full of protein, you experience dizziness, lightheadedness or nausea, you may want to reconsider including the protein shake in your diet.

Although there's no research that directly connects protein shakes to adverse symptoms like these, it's possible that you're allergic to something in the shake or you're just not eating enough, especially if you're trying to lose weight.

You may also be experiencing reactive hypoglycemia or postprandial hypotension, two medical conditions that may need further investigation.

When drinking a protein shake or using protein powder results in lightheadedness or sickness, the first thing you may want to consider is an underlying food allergy. Symptoms of a food allergy — and the intensity of those symptoms — can vary greatly, but in addition to lightheadedness and nausea, you may also experience:

• Coughing
• Swelling of the tongue
• Wheezing
• Hives/rashes
• Runny nose
• Sneezing
• Bloating
• Diarrhea
• Chest tightness
• Loss of breath
• Anxiety/impending doom

If any of these symptoms develop, seek emergency medical attention to rule out a life-threatening allergy. If you're aware of an allergy you already have, check the ingredient list to make sure the protein powder or shake doesn't contain the triggering ingredient. Even if you checked the ingredients when you had it before, look again. Manufacturers sometimes change ingredients without notice.

If you're unaware of any allergies you have, you may want to see an allergy specialist to check for responses to common allergens, especially if there are other foods that make you dizzy. This can be done through a simple prick test or blood test.

Many protein shakes and protein powders are made with some of the most common allergens, like whey or casein from milk, egg and soy. Others, like collagen, may be made from fish or shellfish. If you discover undiagnosed allergies, it's possible that you're allergic to more than one type of these common allergens, so you may have to switch the type of protein shake you drink.

When you're incorporating protein shakes into your diet as part of a weight-loss regimen, it's important to make sure that you're eating enough. If you restrict calories too much or use protein shakes as a meal replacement without making sure they're properly balanced, it can cause low blood sugar, which is characterized by lightheadedness and nausea along with a wide range of other symptoms, like:

• Shakiness
• Anxiety and nervousness
• Hunger
• Confusion
• Increased heart rate
• Fatigue/weakness
• Headache
• Blurred vision
• Pale skin
• Numbness and tingling in the lips, tongue or cheeks

According to Dr. Shamai Grossman, an associate professor of emergency medicine at Harvard Medical School, when you don't eat enough and you have low blood sugar, your body slows down all of its systems to conserve energy. This affects the brain, too, which can make you feel lightheaded and woozy. If you suspect low blood sugar, check your daily food intake and make sure you're eating enough.

Read more: 5 Tips for Eating Protein the Right Way

It's common to drink a protein shake immediately following exercise to replenish muscles and provide the body with post-workout fuel, but if you drink it too soon after working out, it might make you feel sick. According to a report published in Sports Medicine in May 2014, when you exercise, your body reduces the amount of blood flow to your digestive system in an effort to provide your muscles with the blood they need to power through a workout.

As a result, the muscular contractions, or peristalsis, that push food through the digestive tract move slower and gastric emptying is delayed. In other words, during and immediately following exercise, your digestion is slowed down and anything you eat or drink stays in your digestive system longer. If you drink a protein shake too quickly after your workout, it can sit in your stomach and cause symptoms like nausea, vomiting, abdominal pain and diarrhea.

The report mentions that this effect is more commonly seen in high-intensity exercises, like sprints, or endurance exercise, like marathon running, and isn't as common following low- to moderate-intensity workouts. And keep in mind that it's only temporary. Once blood flow returns to normal, so does your digestion. What's more, over the long term, exercise improves bowel function.

Read more: Feeling Dizzy or Lightheaded After Running

If you feel lightheaded or sick after having protein shakes or lots of other foods make you dizzy, you may also have one of two underlying medical conditions — postprandial hypotension or reactive hypoglycemia.

Postprandial hypotension simply means you have low blood pressure after eating. According to Harvard Health Publishing, it's actually common in older adults. Because blood flow to the stomach and small intestine increases when you eat, the heart beats faster to maintain blood pressure to compensate for this increased blood flow.

However, in about one-third of older adults, this process doesn't happen as it should. After a meal, blood flow to the digestive system increases, but the heart doesn't pump faster to compensate. As a result, blood pressure drops and can cause lightheadedness, dizziness, nausea, chest pain and vision troubles around 30 to 60 minutes after a meal.

Similar to postprandial hypotension, reactive hypoglycemia occurs shortly after eating a meal or, in this case, drinking a protein shake. Reactive hypoglycemia refers to low blood sugar following a meal — usually within four hours. Diabetes is a common cause of reactive hypoglycemia, but it can also occur in people who don't have the metabolic condition.

Reactive hypoglycemia can cause all of the same symptoms as low blood sugar, except it occurs in response to a meal, rather than as a result of too much calorie restriction. If you find that protein shakes and dizziness go hand in hand, check with your doctor for a medical evaluation to rule out or confirm any underlying medical conditions.